Magnetic transducing unit



July 6, 1954 G. J. SALIBA ET AL 2,683,038

MAGNETIC TRANSDUCING UNIT Filed Sept. 15, 1948 2 Sheets-Sheet 1 July 6, 1954 G. J. SAMBA ET Al. 2,683,038

' MAGNETIC TRANSDUCING UNIT Filed sept. 15, 194e 2 sheets-sheet 2 ATTO/@Alfy ducing medium could be used. f Y

Patented July 6, 1954 UNITED STATES ATENT OFFICE MAGNETIC TRAN SDUCIN G UNIT George J. Saliba, Englewood, N. J., and Morris .M. Gruber, New York, N. Y., assignors to Presto Recording Corporation, Hackensack, N. J., a

corporation of New York Application September 15,1948, Serial No. 49,7438

particular to such a unit which employs a cylin-` drical shaped recording medium.

By the term transducing in this specification is meant the transformation of sound into an alteration of magnetic status of the suitable recording medium (recording) and/or the transformation of such varying magnetic status into sound (reproduction).

Transducing units operating on the magnetic principle have been known for some time. The transducing medium employed has taken a variety of forms. The most conventional recording media are in the form of magnetizable wires or tapes, and disc-like magnetic records have also been extensively employed. It has in the past been proposed to employ cylindrical magnetic 'transducmg media of a type similar in shape to the early cylindrical gramaphone records but this type of recording medium has not met with acceptance because the cylindrical medium itself was of cumbersome and expensive construction and because no suitable transducing unit had been devised with which such a cylindrical trans- Of prime importance in the design of such a transducing unit is the design of fthe transdu'cing head employed therein. While various types of heads have been proposed for'use with such cylindrical; magnetic transducing media, none known to applicants have met the exacting requirements of precision use, and in particular none have achieved (l) accuracy' of electric to magnetic transformation or viceversa, (2) ready oonformability to the cylindrical transducing surface, 3) `ready removability from that surface to permit interchanging of the cylindrical transducing media, (4) simple manual movability from one position on the magnetic transducing surface to another so as to selectively record, reproduce or erase any desired portion of the magnetic media, and (5) proper location of the erasing head with respect to the transducing head so as to ensure no magnetic interference between the two but effective operation of both.

The prime object of the present invention is to devise a transducing unit which will achieve the advantageous results set forth above with regard to the transducing head thereof.

Another object of the present invention is to devise a compact transduci'ng unit adapted to employ cylindrical recording media and to cooperate therewith in a precision-like manner vso as to record or reproduce the same and so as to permit the cylindrical transducing media to be readily, interchangeable one with the other.

To the accomplishment of the foregoing 'ob- `jects and such other objects as may hereinafter appear, the present invention relates to the transducing unit and a cylindrical magnetic transducing medium employed therewith as defined in the appended claims and as set forth in this specication, taken together with the accompanying drawings, in which;

Fig. 1 is a top View of the transducing unit of the present invention, the cylindrical magnetic transducing medium and the transducing head being omitted therefrom;

Fig. 2 is a side cross-sectional view taken along the line 2-2 of Fig. l but showing a cylindrical -transducing medium and head, portions of said transducing medium being broken away to eX- pose said head, and the rotative mounting for the feed means also being 'shown in crossesection;

f Fig. 3 is an end cross-sectional view-taken along the line y3--3 of Fig. 2, the positions of the motor and the transducing medium being shown in broken lines; f

Fig. 4 is aside View on an enlarged scale of the transducing head construction ofthe unit vshowing that head` in transducing position on Athe cylindrical magnetic transducing medium;

Fig. 5 Vis -a view showing the transducinghea in frontelevation on an enlarged scale. j i

The transducing unit vof the present invention comprises aY frame generally designated 2 on which is mounted a motor 1i, the motor driving a rotatable feed element 5 for a transducing head generally designated 8 and also drivinga combination centering and driving device iii engageable with one end of a cylindrical transducing medium generally designated l2. As the transducing medium I2 is rotated, the transducing head 8 is moved across the magnetizable surface thereof preferably in a direction parallel to the 'axis thereof, the head 8 therefore magnetizing or cooperating with the magnetic status of the transducing unit I2 over a helical path.

The frame is 'provided with side walls Ill and i6 and end walls I8 and 2i). Bars 22 and 24 extend between the side 'walls Il and i6 supported by ledges v2li and the motor i is supported on said bars 22 and 24 via supporting plate Si] to which the motor is fastened by means of bolts 32 and washers T34 (see particularly Fig. 2). A roof 36, which may be an 'extension of and integrally formed with the side wall I4, may be provided to extend over the motor 4 and hide the same from view from above (see Fig. 1). This roof terminates at 38 short of the rotatable feed element 6 in order to expose the transducing head 8 and the transducing medium i2, so that they may be readily manipulated.

A shaft 40 is driven at one end by the motor 4 and has its other end journalled in side wall 28. at 42. A worm 44 is fastened thereto, the worm meshing with and driving worm wheel 46 attached to shaft 48 and journalled in bearing 50 fastened by means of bracket =52 to the side wall 20. The shaft 48 extends in a direction at right angles to the shaft '40 and has its other end journalled in bearing 54 attached to side wall by means of bracket 56. The shaft 48 has attached thereto at positions appropriately spaced along its length a pair of hubbed gears 58 and 60. The shaft 48 may if desired be formed in a plurality of sections, these sections being joined by adjustable coupling 62.

The gear 58 meshes with and drives gear 64 which is in turn attached to shaft 66 one end of which is journalled in bearing 68 attached to side wall 20 and the other end of which is journalled in side wall I8 where it is joined with adjustment knob 18 which projects out past the side wall I8. The knob 10 rotates with the shaft 66 and is made accessible so that any given rotative position of the shaft 66 may be achieved independently of the motor 4. The shaft 66 carries the rotatable feed element 6, that element being here disclosed in the form of a helical feed screw the threaded portion of which denes a feed groove adapted to move the transducing head 8 across the transducing medium I2.

The gear 68 meshes with and drives gear 12 which is in turn fastened to stub shaft 14 mounted in bearing 16 in the side wall 26. The end of the shaft 14 opposite from the bearing 16 has attached thereto centering and driving unit I IJ, this unit being in the form of a disc having a tapered projection 18 axially disposed thereon and having a pin 80 projecting from its inner surface at a point radially disposed from the axial projection 18. As will become apparent hereinafter, the projection 18 is adapted to cooperate with the cylindrical magnetic transducing medium I2 so as to center the same and the pin 80 is adapted to cooperate with the transducing medium I2 so as to rotate the same. It will be apparent that inasmuch as the single drive shaft 48 simultaneously rotates both the feed element 6 for the transducing head 8 and,

Via the driving unit I0, the transducing medium I2, the transducing head will be caused to move across the surface of the transducing medium I2 in a direction parallel to that of the shaft 86 and consequently parallel to the axis of the transducing medium I2 while the transducing medium I2 is rotating about its own axis.

The transducing unit and centering unit 8| active to support the end of the transducing unit I2 opposite from that engageable with the centering and driving unit |0 is mounted in the side wall I8 opposite the centering and driving unit I0. This unit 8| comprises a plunger 82 the inner projecting end of which is provided with a portion 84 of increased diameter and a tapered projection 86 which is accurately positioned opposite the projection 18 so that a line drawn between the tips of the projections 18 and 86 will be parallel to the shaft 66 and the rotata- 'ble feed element 6 for the transducing head 8.

The plunger is slidable within bushing 88 pressfitted in bearing 98 in the side wall I8, a spring 92 being secured within the bushing and active upon the large diameter portion 84 of the plunger 32 so as to urge the same inwardly. The outer projecting end 94 of the plunger 82 is fastened to pull knob 96, the knob serving to limit inward motion of the plunger 82 and to provide a manual means for moving the plunger outwardly, i. e., to the right as viewed in Fig. 2, when interchanging the transducing media I2.

A-pair of rods 88 and |68 are secured between the side walls |8 and 28 and beneath the cylindrical transducing medium I2, the spacing being such that when the transducing medium I2 is properly mounted on and between the centering and driving unit I0 and the centering unit 8|, there will be a slight but definite clearance between the transducing medium I2 and the rods 88 and |08 (see Fig. 3) so that the transducing medium, when rotated, will be rotatable free of frictional retardation. However, it is desirable that the rods 98 and |08 be placed Very close to a position in which they will make contact with the mounted transducing medium I2 so that should the medium I2 be accidentally disengaged from its centering and driving units, or should those units be improperly engaged with the rnedium I2, the medium I2 will nevertheless be retained in a close to operative position, thus preventing accidental dropping of the medium I2. Moreover, if the medium l2 be initially placed upon. the rods 88 and |86, Vthe latter define a support for the unmounted medium I 2 which places that medium in a position closely adjacent to its proper mounted position, thus facilitating engagement between the medium I2 and its cooperating centering and driving units I8 and 8 I.

The transducing head of the instant transducing unit (see Figs. 2, 4, and 5) presents many desirable constructional features. This unit comprises a body |82, here shown as roughly1 triangular in cross-section, which is provided with an aperture |84 through which rod It@ passes, at least a portion. of the shaft IE5 being keyed, as at |01, to prevent the body |02 from rotating thereon, the body |62 being slidable over the shaft |88 and the shaft ills thereby defining a support for the body` |82 along which that body is movable. Articulately attached to the body |62 by means of pins |88 engageable with trunnions H8 is a feed groove engaging member ||2 carrying atone end a knife edge H4 adapted to t into the helical feed groove or screw thread in the feed screw Theother-end of the groove engaging member I|2 is provided with a finger piece |56 and the body |82 is provided with a cooperating opposing finger piece H8. A spring |28 is housed within. recesses |22 and |28 in the finger pieces IE5 and IIB respectively, the spring |20 being maintained under compression so as to urge the two finger pieces IIE and H8 apart, thus tending to rotate the groove engaging member I I2 in a counter-clockwise direction as viewed in Fig. 4 so as to cause the knife edge H4 to engage with the feed screw 6. 1t will be apparent that when this normal condition obtains, rotation of the feed screw 6 will cause the knife edge |I4 to move along the axis of the screw 6 and since the body |02 is slidable on the shaft |86, the body |02 will be correspondingly moved. Thus, accurate control ,of the translation of the body |82 is achieved, this control being just as fine and accurate as the cutting of the feed screw therefrom.

6. It wil1 also be clear that by pressure applied to the nger pieces ||6 and I8 in a direction to compress the spring |20, the groove engaging member ||2 will be rotated in a clockwise direction as viewed in Fig. 4, thus disengaging the yknife edge 4 from the feed screw 6, thereby permitting the body |02 to be manually slid along the shaft |06 to any` desired position. By this simple structure, the transducing head 8, which is attached to the body |02, is either fed along the surface of the transducing medium I2 by the feed screw 6 so that its pole pieces trace a helical path thereover, or the transducing head 8 may be manually positioned at anyappropriate and desired point along the length of the transducing medium I2.

Since the surface of the medium I2 is cylindrical, and since it is essential, for clarity and fidelity of reproduction and recordation, that the magnetic heads, and particularlythe pole pieces thereof, be accurately positioned with respect to the transducing cylinder I2, the manner of connecting the head 8 to the body |02 which is moved by the feed screw is of considerable importance. vThe present invention has combined this manner of connection with the particular construction of the head 8 so as to achieve the desirable advantages set forth at the beginning of this specification.

A linking element |26 is pivotallyattached to the body |02 by means of pins |28, the element |26 Yextending over the transducing cylinder 2 and being provided with a, projecting finger piece |30. The transducing head housing |3| is pendulously mounted from the linking element |26, the pins |32 in the linking element |26 cooperating with trunnions |34 which may be integral with the housing |3| and connected thereto by means of neck |36 which passes up into the linking element |26. Set screws |38 may be provided to secure the pins |32 in position and similar set screws may be employed with the pins |08 and |28 as Well. v A

The housing |3| contains within itself a pair of magnetic units, one defining an erasing head l|40 and the other defining a transducing, or recording and reproducing head 42. Each of these heads contains a Vpair of pole pieces |44 and '|46 respectively, an air gap|48 being provided between each of the pole piece pairs." The tips of the pole pieces |44 and |46 project belowthe head structure 6 so asl to be either 'directly engageable with the; surface ofjthe transducing medium l2, or to be positionable a fixed distance It has been found to be most de-l sirable to have these two pair of pole pieces |44 and |46 eduidistant from the magnetizable sur- .face of the transducing medium |2. It is also necessary that the pole pieces |44 and |46 be spaced from one another sufficiently so that the magnetic effect of Yone will not unfavorably affect'the magnetic'eiect of the other. Moreover, particularly during recording, it is essential that the pole pieces |44 of the erasing head |40 traverse a particular segment of the magnetizable surface before that segment is traversed by the pole pieces |46 of the transducing head |42 since al1 prior recordings must be erased before the new recording is magnetically placed thereon. The illustrated construction involves a spacing and positioning of the heads |40 and |42 together with their respective pole pieces |44 and |46 in order to achieve the above results.

The projecting tips of the pole pieces |44 and n |46 are spaced from one another in two directions.

As may be seen in Fig. 4, the pole pieces `are segment of the transducing medium before the transducing head |42. In order to ensure adequate spacing between the two heads, the pole pieces |44 are also spaced from the pole pieces4 .|46in the direction of motion of the body |62.

As may be best seen in Figs. 2 and 5, the body |62 and the transducing head 8 of which it is a part, are adapted to move in the direction of the arrow n |56. Consequently, the projecting tips of the pole pieces |44 of the erasing head |40 are positioned in advance of the projecting tips of the pole pieces |46 of the transducing head |42. It will, of course, be obvious that the amount of this spacing may be varied within considerable limits, it being necessary only that the spacing be so related to the pitch of the feed groove in the feed screw 6 that a portion of the magnetizable surface of the transducing medium f I |2 to be traversed by the pole pieces |44 will also be traversed by the pole pieces |46 and that the spacing be suiicient so that deleterious magnetic interaction between the pole pieces |44 and |46 be avoided.

In order to permit the pole pieces |44 and |46 to be equidistantly positioned with regard to the magnetizable surface of the transducing medium I2, they are positioned along van arc of said magnetizable surface. The pendulous articulate mounting of the head housing |3| from the linking element |26 permits accurate conformabilit'y of the pole pieces |44 and |46 to the cylinder I2. The articulate mounting of the linking element |26 on the body E02 permits that element and the head structure 8 to be bodily raised from the transducing medium |2 so as to facilitate the replacement of said medium. In this regard it should be noted that the finger piece |30, shown on the vlinking element |26, might equally well be'placed on the housing ISI.

. Themagnetic transducing medium |2 itself is best illustrated in Fig. 2. It comprises an openended cylindrical structural frame |52 which may either itself be of magnetizable material or which may be of any suitable structural material having a magnetizable coating thereon. A pair of `plugs |54 and |56 are provided to close the open ends of Vthe cylindrical structure |52 and each of these plugs are provided, at points accurately corresponding to the central axis of the cylinder, with recesses |58 and |60 cooperating respectivelyv with the projections I8 and 66 on the centering and driving unit l0 and the cente ing unit 6| respectively. One of tht plugs, here shown as |56, has an additional aperture |62, radially spaced from the aperture |58 and adaptedl to receive the pin 60 of the centering and driving unit II).

As disclosed in Fig. 2, accurate centeringV of the transducing unit l2 is achieved together with structural rigidication thereof and particularly rigidication with regard to the inwardly directed forces exerted by the projections i8 and 86, by shaft |64, which extends between and projects through the plugs 54 and 56, being retained in rigid connection therewith by means of set screws |66, theshaft |64 being provided with precision located recesses |58 and |60. By means of this construction, fabrication of the various component parts of the transducing medium |2 is facilitated, and the shaft |64, preferably of steel or other structural metal, takes and successfully resists all of the compressive forces exerted by the spring 92, thus permittingr the cylindrical surface of the structural frame |52 to maintain its true structural shape free of pressure-induced distortions.

The operation of the transducing unit here disclosed will in the main be apparent from the above structural description. When a cylinder I2 is to be inserted into the device, the iinger piece |30 on the linking element |26 is lifted so as to move the head housing |31 out of the way, the cylinder |2 is placed on the rods 98 and |00, the button 96 is withdrawn so as to move the plunger 82 and the projection 66 outwardly, and the opposite end of the cylinder l2 is lifted and rotated so that the pin 80 is received within the recess |62 and the projection 18 is received Within the recess |58. The button 96 is then released and the cylinder I2 is adjusted until the projection 86 is received Within the recess |60. The head housing |3| is then lowered until the pole piece tips |44 and |46 make contact with the magnetizable surface of the cylinder l2, the connection of the housing |3| to the body |62 easily permitting conformance of the pole piece tips |44 and |46 to said magnetizable suriface. The finger pieces ||6 and ||8 are compressed so as to disengage the knife edge ||4 from the feed screw 6 and the head is then positioned at any desired point along the magnetizable medium. The motor is then started so that the cylinder I2 is rotated and the head 8 is fed along the length of the cylinder, the pole pieces |44 and |46 describinga helical path thereover, so as to either record or reproduce along said helical path. The electric and magnetic circuits involved in this recording and reproducing may take any one of a number of well known forms and constitute no part of the present invention.

If reproduction of only a portion of the recording is to be repeated, it is necessary merely to compress the finger pieces ||6 and i IB and slide the body |62 along the shaft |66 to the desired position. It is preferable, before performing this operation, if the pole pieces |44 and |46 are in direct contact with the cylinder |2, to lift them therefrom by means of the finger piece |30 in order to eliminate frictional forces thereon whichl might tend either to break the pole pieces |44 and M6 or to mar the magnetizable surface of the cylinder.

Other modes of manipulation of the apparatus will suggest themselves,

By the construction above described, there has been provided a transducing unit capable of e'iciently and accurately employing a cylindrical magnetic transducing medium and an improved construction of said transducing medium has also been disclosed. While only one embodiment of this invention has been here disclosed, it will be apparent that many changes may be made in its construction without departing from the spirit of the invention as defined in the appended claims.

We claim:

l. A magnetic transducing head structure for use with a cylindrical magnetic recording medium comprising a body movable in the direction of the axis of the recording medium and having an aperture for receiving a support along which said body is movable, a pole piece housing articulately attached to said body by means of a linkage having a plurality of pivots extending collaterally of the axis of the recording medium so as to be conformable to the surface of said recording medium, a finger piece for moving said housing toward and away from said recording medium, and a transducing head and an erasing head in said housing, said heads having pole pieces spaced from one another in the direction of the axial motion of said body, said erasing' head pole piece being advanced in the direction of motion of said body with respect to said transducing head pole piece.

2. A magnetic transducing head structure for use with a cylindrical magnetic recording medium comprising a body movable in the direction of the axis of the recording medium and having an aperture for receiving a support along which said body is movable, a pole piece housing articulately attached to said body by means of a linkage having a plurality of pivots extending colv laterally of the axis of the recording medium so as to be conformable to the surface of said recording medium, a finger piece for moving said housing toward and away from said recording medium, and a transducing head and an erasing head in said housing, said heads having pole pieces spaced from one another in the direction of rotation of said cylindrical transducing medium, and also spaced from one another in the direction of the axial motion of said body, said erasing head pole piece being advanced in the direction of motion of said body with respect to said transducing head pole piece.

3. A magnetic transducing head structure for use with a cylindrical magnetic recording medium comprising a body movable in the direction of the axis of the recording medium and having an aperture for receiving a support along which said body is movable, a pole piece housing articulately attached to said body by means of a linkage having a plurality of pivots extending col- 1iaterally of the axis of the recording medium so as to be conformable to the surface of said recording medium, a finger piece for moving said housing toward and away from said recording medium, and transducing head and an erasing head in said housing, said heads having pole pieces and said pole pieces having tips which engage said recording medium, said tips being spaced from one another in the direction of rotation of said-cylindrical transducing medium and also spaced from one another in the direction of the axial motion of said body, said erasing tip being advanced in the direction of motion of said body with respect to said transducing tip.

zi. A magnetic transducing head structure for use with a cylindrical magnetic recording medium comprising a body disposed over the recording medium and movable in the direction of the axis of rotation of the recording medium, a linking member pivotally mounted on said body and extending over said cylindrical recording medium in a direction transverse to the axis of the recording medium, a pole piece housing pendulousiy mounted on said linking member on an axis extending in the direction of the axis of the recording medium, said housing carrying a transducing head and an erasing head, said heads having pole pieces the tips of which are adapted to be positionable closely adjacent to the cylindrical recording surface and which are spaced from one another around the periphery of the recording medium, said pole pieces being spaced from one anotherin the direction of the axial motion of said body, with said erasing head pole finger piece on said linking member located over Said recording medium and said housing for ready accessaoility for moving said housing toward and away from said recording medium, the mounting being such that said pole pieces are permitted to ireeiy conform to said cylindrical recording surface when positioned closely adjacent thereto.

5. A magnetic transducing head structure for use with a cylindrical magnetic recording medium comprising a body disposed over the recording medium and movable in the direction of the axis of rotation of the recording medium, a linking member pivotally mounted on said body and extending over said cylindrical recording medium in a direction transverse to the axis of the recording medium, a pcie piece housing pendu-- lously mounted on said linking member on an axis extending in the direction of the axis of the recording medium, said housing carrying a transducing head and an erasing head, said heads having pcie pieces the tips of which are adapted to be positionaole closely adjacent to the cylindrical recording surface and which are spaced from one another around the periphery of the recording medium, said pole pieces being spaced one another in the direction of rotation of said cylindrical recording medium and spaced from one another in the direction of the axial motion of said body, said erasing head pole piece 1oeing advanced in the direction of rotation and in the direction of motion of said body with respect to said transducing head pole piece, and

an outwardly projecting finger piece on said linking member located over said recording me dium and said housing for ready accessability for moving said housing toward and away from said recording medium, the mounting being such that said pole pieces are permitted to freely conform to said cylindrical recording surface When positioned closely adjacent thereto.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 511,402 Bruening Dec. 26, 1893 661,619 Poulsen Nov. 13, 1900 746,609 Vogel Dec. 8, 1903 760,655 Solon May 24, 1904 819,670 Pedersen May 1, 1906 398,283 Stuart Sept. 8, 1908 1,049,237 Holland Dec. 31, 1912 1,100,024 MacDonald June 16, 1914 1,754,454 Bodine Apr. l5, 1930 1,785,409 Frykman Dec. 16, 1930 1,973,081 Keiser Sept. 11, 1934 2,220,620 Somers et al. Nov. 5, 1940 2,229,293 Huntley et al. Jan. 21, 1941 2,279,227 Dunning et a1. Apr. 7, 1942 2,530,029 Pond Nov. 14, 1950 2,538,452 Harrington Jan. 16, 1951 2,548,831 Trevitt et a1 Apr. 10, 1951 2,573,303 Bozoky Oct. 30, 1951 FOREIGN PATENTS Number Country Date 394,884 Germany May 12, 1924 

